Enthalpy and entropy definitions (paper 1/3)

Question 1

Enthalpy change of formation

Answer 1

enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions
- EXOTHERMIC - energy is released when bonds form
2C(s) + 3H2(g) + 1⁄2O2(g) ➔ C2H5OH(l)

Question 2

Enthalpy change of atomisation

Answer 2

enthalpy change when one mole of gaseous atoms is formed from the element in its standard state under standard conditions
- ENDOTHERMIC - energy is required for bond breaking
1⁄2Cl2(g) ➔ Cl(g)

Question 3

first ionisation energy

Answer 3

enthalpy change when one mole of gaseous 1+ ions is formed from one mole of gaseous atoms
- ENDOTHERMIC - need to overcome electrostatic attraction between electron and nucleus
Mg(g) ➔ Mg+(g) + e-

Question 4

second ionisation energy

Answer 4

enthalpy change when one mole of gaseous 2+ ions is formed from one mole of gaseous 1+ ions
-ENDOTHERMIC
Mg+(g) ➔ Mg2+(g) + e-

Question 5

first electron affinity

Answer 5

enthalpy change when one mole of gaseous 1- ions is formed from one mole of gaseous atoms
- EXOTHERMIC
O(g) + e- ➔ O-(g)

Question 6

second electron affinity

Answer 6

enthalpy change when one mole of gaseous 2- ions is formed from one mole of gaseous 1- ions
- ENDOTHERMIC - energy must be supplied to overcome the repulsion between the negative ion and the incoming election
O-(g) + e- ➔ O2-(g)

Question 7

bond enthalpy

Answer 7

enthalpy change when one mole of a particular covalent bond in the gaseous state is broken
Cl2(g) ➔ 2Cl(g)

Question 8

lattice enthalpy

Answer 8

measure of the strength of ionic bonding in a giant ionic lattice - enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions under standard conditions

Question 9

enthalpy change of hydration

Answer 9

enthalpy change when one mole of aqueous ions is formed from one mole of gaseous ions
Li+(g) ➔ Li+(aq)
- ALWAYS EXOTHERMIC

Question 10

enthalpy change of solution

Answer 10

enthalpy change when one mole of a solute is dissolved in sufficient water to form a very dilute solution
LiCl(s) ➔ LiCl(aq)

Question 11

enthalpy change of combustion

Answer 11

enthalpy change when one mole of a substance combusts fully in oxygen under standard conditions
CH4(g) + 2O2(g) ➔ CO2(g) + 2H2O(l) ΔH⦵c = 890 kJ mol-1.

Question 12

enthalpy change of neutralisation

Answer 12

enthalpy change when an acid and a base neutralise under standard conditions, to form one mole of water
HCl(aq) + NaOH(aq) ➔ NaCl(aq) + H2O(l) ΔH⦵neut = 57 kJ mol-1.

Question 13

standard conditions for enthalpy change

Answer 13

298K, 101kPa

Question 14

standard entropy

Answer 14

entropy of one mole of a substance under standard conditions

Question 15

entropy

Answer 15

the measure of the disorder of a system

Question 16

spontaneous reaction

Answer 16

a reaction which can occur at the specified temperature without a constant input of energy